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Best solution for primary distribution in residential property

Alan B

I am looking at a project in a fairly large residential property and trying to avoid a collection of small consumer units near the supply head.

Supply is TNCS, no measurements at this stage

The supply head is in an external meter box, I will be putting an additional box of some sort next to it.

Based on a rough initial plan, from the meter head there will be the following connections

60A sub main on 16mm SWA to main house DB

60A sub main on 16mm SWA to garage, feeding two EV chargers with load management on main feed and garage submain.

Assuming 16A connection on 10mm cable to solar panels in field 30 to 50m away

Assuming 16A connection to battery inverter 5m away

House is on fused connection taken from henley blocks in main meter box, plan to leave this as it is and then run tails from henley blocks to second meter box.

Question is what do I do there to support the 3 connections

Initial thought has been an IP65 enclosure with 3 MCB's, but then I have some concerns

  • I don't think I can get an IP65 enclosure with a busbar capable of supporting 16mm cable for the load and MCB's for each of the circuits, with spare slots for future expansion
  • Cables will be armoured clipped direct or underground in ducting
  • Beginning to think a fused switch  might be better for the garage to provide better selectivity, downside is that I will end up with an enclosure for each submain?

VD on garage submain 1.36% and for a 63A fuse with 5 second disconnect time max earth fault loop impedance is achievable at 1.07 ohms. DB in garage will be all RCBO. Garage will be a TT island

Solar and battery system not my responsibility but trying to take a holistic view on design of distribution at the supply head

Are there better ways to do this, enclosures that support cartridge fuses and circuit breakers, just go with metal CU in IP65 enclosure.

Given that the meter head is actually in an open log store next to the house I am swaying towards everything going inside a metal IP65 enclosure

Welcome your thoughts

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    I also wonder how they would handle sitting at full load for 12 plus hours with a couple of cars charging.

    KMF type switchfuses have been used for donkey's years to supply complete installations - including some with night storage heaters, which are probably as bad if not worse than EVs -  without any problems that I have heard of.

    In some ways using mcb's has it's appeal because presumably they won't generate as much heat when running close to limits. If a C curve was used what's the chance of nuisance tripping.

    MCBs have in-built thermal elements (in effect a small heater wrapped around a bimetallic strip) - so certainly not free of the self-heating problems. I'd have to check some manufacturer's data for actual figures, but I doubt it's massively better than a good HBC fuse.

    The curve type (B,C,D) doesn't make much difference at all to the overload behaviour of an MCB - the thermal response is normally the same - the difference is just the point where the 'instantaneous' magnetic trip takes over. E.g.

       - Andy.

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    I also wonder how they would handle sitting at full load for 12 plus hours with a couple of cars charging.

    KMF type switchfuses have been used for donkey's years to supply complete installations - including some with night storage heaters, which are probably as bad if not worse than EVs -  without any problems that I have heard of.

    In some ways using mcb's has it's appeal because presumably they won't generate as much heat when running close to limits. If a C curve was used what's the chance of nuisance tripping.

    MCBs have in-built thermal elements (in effect a small heater wrapped around a bimetallic strip) - so certainly not free of the self-heating problems. I'd have to check some manufacturer's data for actual figures, but I doubt it's massively better than a good HBC fuse.

    The curve type (B,C,D) doesn't make much difference at all to the overload behaviour of an MCB - the thermal response is normally the same - the difference is just the point where the 'instantaneous' magnetic trip takes over. E.g.

       - Andy.

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